This invention relates to accelerometers.
Accelerometers generally have a seismic mass that is mounted for displacement under the forces caused by acceleration. Displacement of the mass is sensed by a pick-off, and a restoring force is applied to the mass to restore it to its datum position, in a servo manner. By measuring the restoring force, an indication of acceleration can be provided.
In one form of conventional accelerometer, the seismic mass is provided by a cylindrical coil that is mounted for displacement along the length of an axiallypolarized cylindrical permanent magnet. The mounting is achieved by an arm tht projects radially from the coil and that is pivoted about an axis at right angles to the axes of the coil and of the arm. A conventional pickoff senses displacement of the arm and supplied signals via a feedback circuit to the coil such that the magnetic field produced by the coil interacts with that of the magnet in a sense to restore the coil to its datum position. Measuring the current supplied to the coil provides an indication of the component of acceleration acting on the accelerometer along the coil axis.
While such accelerometers can function satisfactorily, the configuration of the coil and its mounting makes it somewhat bulky. The configuration of the coil and the permanent magnet also leads to considerable stray magnetic fields and a relatively low efficiency.